1. Field of the Invention
The present invention relates to a write driver circuit for driving a magnetic head and a hard disk apparatus incorporating the same.
2. Description of the Related Art
In recent years, storage devices using magnetic storage media, such as hard disks, are becoming more and more popular as one of storage devices for storing a large volume of data along with the widespread use of computers. In these magnetic storage devices, a write operation into a magnetic storage medium is accomplished by supplying a write current, which corresponds to data to be stored and which is generated by a write driver circuit for driving a magnetic head, to a magnetic head placed in close proximity to the magnetic storage medium, to thereby magnetize a predetermined storage area of the magnetic storage medium in a predetermined direction by the magnetic head.
One conventional popular example of the write driver circuit for driving a magnetic head is one that instantaneously increases (overshoots) the write current by instantaneously superposing an overshoot current onto the write current only when the direction of magnetization is changed. The reason why the write current is overshot at the time of changing the direction of magnetization is that it is advantageous in ensuring correct magnetization of the storage area in the magnetic storage medium immediately after the current supply to the magnetic head, which successfully clarifies the timing when the direction of magnetization is changed, and improves jitter characteristics when stored data is read from the magnetic storage medium. An exemplary configuration of the circuit is shown in FIG. 4.
A conventional write driver circuit 100 for driving a magnetic head shown in FIG. 4 includes a write current generating section 104 for generating two types of write current (write current for normal rotation and write current for reverse rotation) to be applied to a magnetic head 103 based on write driver control signals 101, 102, a switching signal generating section 107 for generating switching signals 105, 106 for selecting either one of the two write currents, a switching section 108 for switching the write currents according to the switching signals 105, 106, and an overshoot current generating section 109 for generating an overshoot current for instantaneously increasing the write current when the direction of magnetization is changed.
The overshoot current generating section 109 is designed to generate an overshoot current according to voltage changes in the switching signals 105, 106 generated by the switching section 108 when the direction of magnetization is changed, and to output the thus generated overshoot current towards the write current generating section 104. This allows the write driver circuit 100 for driving a magnetic head to supply a write current having superposed thereon the overshoot current from the write current generating section 104 to the magnetic head 103.
As described in the above, the conventional write driver circuit 100 for driving a magnetic head is configured so that the overshoot current generating section 109 generates the overshoot current based on the voltage changes in the switching signals 105, 106 used for switching the write current in the switching section 108.
As a consequence, the current value of the overshoot current generated by the overshoot current generating section 109 is determined by the voltage level of the switching signals 105, 106, the capacity of capacitors 114, 115, the resistance of resistors 112, 113, and so forth, and is thus always keep at a constant value.
That is, the conventional write driver circuit 100 for driving a magnetic head is configured so as to allow the overshoot current generating section 109 to generate the overshoot current always at a constant level when the direction of magnetization is changed by the switching section 108, and to allow such constant overshoot current to be output towards the write current generating section 104 to thereby instantaneously increase the write current generated therein.
The conventional write driver circuit 100 for driving a magnetic head is, however, disadvantageous in that the current value of the overshoot current is always kept constant while being governed by the voltage level of the switching signals 105, 106, the capacity of the capacitors 114, 115 and so forth, which makes it difficult to conveniently apply the circuit to plural types of magnetic heads or magnetic storage media. In other words, since magnetic heads or magnetic storage media differ individually from each other according to their materials and electrical properties, and as a consequence, differ significantly with each other in optimum values for the overshoot current, a circuit having only a single constant value for the overshoot current is not applicable to the entire range of the magnetic heads or magnetic storage media.
In particular, since the conventional write driver circuit 100 for driving a magnetic head described above is designed to generate the overshoot current based on voltage changes in the switching signals 105, 106 used for switching the write current in the switching section 108, it is fairly difficult to apply the circuit to plural kinds of magnetic heads or magnetic storage media. This is because an allowable range for the voltage changes in the switching signals 105, 106 should fall within a predetermined range given by a circuit configuration of the switching section 108, so that the generation of the overshoot current based on voltage changes in the switching signals 105, 106 inevitably limits the variable range of the overshoot current, which makes it difficult to conveniently apply the circuit to a variety of magnetic heads or magnetic storage media.